FERTILITY INDEX (FI) is a bio-economic index which considers six traits, each trait weighted according to its heritability and economic importance in a cow-calf enterprise. The value is expressed in standard deviation terms, which can be difficult to comprehend. IBBA advises breeders to evaluate the percentile rank rather than the actual index value. BREED BACK (BB) is the probability that a cow will calve as a three-year-old given that she calved first as a two- year-old. AGE AT FIRST CALVING (AFC) is expressed in days, and represents the day a first calf heifer calves compared to her yearling contemporaries. A lower number indicates animals that calve early in their first calving season and is desirable. NUMBER OF CALVES (NC) measures the number of calves a cow has up to 7 ½ years of age. The unit of measure- ment is the actual number of calves. Twins count as one calf. This trait is expressed later in life but is highly cor- related with AFC and BB which are expressed early in life. ACCURACY Accuracy (ACC) values indicate the reliability of the published EPDs for an animal and can be defined as the relationship between the published or listed EPD and the “true” value of the number. Accuracy is primarily based around the information available to calculate a given trait. An older sire with more progeny, genomic testing, and relatives in the database is more likely to have a higher accuracy than an unproven, younger sire simply due to a greater amount of information available. Accuracy is listed on a scale from zero to one. The closer the accuracy is to 1.0, it’s more likely to represent the true genetic merit of the sire. For example, as progeny or genomic tests are re- corded, a sire’s accuracy level should increase for reported traits, while his actual EPD numbers may fluctuate either up or down, or remain static, based on reported data. PERCENTILE RANK Based on percentages, percentile rank indicates where a bull’s EPD ranks him in the entire population of his respec- tive breed. In all cases in this sire directory, the bulls are compared to “active sires,” or sires who have had progeny registered with IBBA recently. Black Brangus and Ultrablack sires are compared against the January 2025 EPD averages of the Active Black Bran- gus Sires list. The Red and Ultrared sires are compared against the January 2025 EPD averages of the Active Red Brangus Sires list. In all cases except birth weight, fat thickness, mature cow weight, and age at first calf the higher the EPD value the lower the percentile rank number. The percentile rank, therefore, represents the percentage of bulls with higher EPDs. A bull with a 5% rank is YW, for example, is in the top 5% of the population for YW. For example, the top 1% of BW for active Brangus sires is -3.3, meaning less than one percent of the breed records a birth weight EPD of -3.3 or less. Conversely, a BW of 3.2 is in the 95th percentile, meaning 95 percent of the breed records a birth weight EPD of lower than 3.2. The 50th percentile represents the breed average for that given EPD trait. ACTUAL PERFORMANCE DATA BIRTH WEIGHT (BW) is recorded in actual pounds of weight measured within 24 hours of birth of the sire listed. WEANING WEIGHT (WW) is recorded in actual pounds of weight measured, averaged to 205 days of age, of the sire listed. YEARLING WEIGHT (YW) is recorded in actual pounds of weight measured, averaged to 365 days of age, of the sire listed. Genetic Partners | Page 8
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